The present invention relates to fluid flow filters, and particularly filters of the screen type which are inserted or assembled into a flow passage for filtering particles of a predetermined minimum size from entering the flow passage. The present invention relates particularly to filtering particles from entering the flow port of a gas valve, for example the type of valve employed for controlling flow of fuel gas to a burner.
Fuel burner gas valves commonly employ a very fine mesh wire screen in the flow port thereof to prevent foreign particles from entering the valve and becoming lodged on the valve seat to prevent sealing of a valve member thereon and corresponding leakage. In providing filter screens in the flow passage for gaseous fluid, problems have been encountered in installing and securing the screen in such a manner as to prevent easy removal of the screen. Heretofore, it has been common practice to form the screen into a cupped configuration with a rolled edge which may then be pressed with an interference fit on the rolled edge into the outlet port of the valve. However, this procedure can result in small slivers of metallic material entering the valve during the screen installation and becoming lodged between the resilient valve member and the valve seat, thereby causing leakage. With reference to FIG. 7 of the drawings, it has also been known to provide a cupped filter screen, and to retain the screen by reversing and deforming metal tabs over the cupped end to prevent removal of the screen. However, neither of the aforesaid known techniques of screen installation have been proven to be sufficiently tamper resistant as to prevent ready removal of the screen when clogged.